Gas turbine engines produce power by extracting energy from a flow of hot gas produced by combustion of fuel in a stream of compressed air. In general, turbine engines have an upstream air compressor coupled to a downstream turbine with a combustion chamber (“combustor”) in between. Energy is released when a mixture of compressed air and fuel is ignited in the combustor. The resulting hot gases are directed over blades of the turbine, spinning the turbine, thereby, producing mechanical power. In typical turbine engines, one or more fuel injectors direct some type of liquid or gaseous hydrocarbon fuel (such, diesel fuel or natural gas) into the combustor for combustion. Some embodiments of fuel injectors are designed to direct both a liquid and a gaseous fuel into the combustor. In these embodiments, the turbine engine may operate on one fuel as the primary fuel with the other fuel used during periods of unavailability of the primary fuel. For example, some gas turbine engines may normally operate on natural gas fuel. In these turbine engines, diesel fuel may be used during-periods of natural gas unavailability. The fuel is mixed with compressed air (from the air compressor), in the fuel injector, and delivered to the combustor for combustion. This compressed air, which may exceed 800° F. (426.7° C.) in temperature, may surround sections of the fuel injector, and may create a hot ambient environment for the fuel injector. Combustion of the fuel in the combustor creates hot gases exceeding 2000° F. (1093.3° C.), which may heat surrounding surfaces. The heat released due to combustion may also heat fuel injectors, which may be coupled to the combustor.
Fuel injectors include fuel lines and fuel galleries that are used to direct the fuel to the fuel injector and deliver the fuel to the combustor. In a fuel injector that is configured to deliver both liquid and gaseous fuel to combustor, separate fuel lines may deliver the liquid and gaseous fuel to the fuel injector. When the turbine engine operates on gaseous fuel, the liquid fuel may remain in the fuel lines and galleries. In some embodiments, the liquid fuel may be purged from the liquid fuel lines and galleries. However, even in these embodiments, the liquid fuel may exist as a coating on these purged lines and galleries. Due to operating conditions of the fuel injector, the liquid fuel in the liquid fuel lines and galleries may be exposed to ambient temperatures of about 500° F.-800° F. (260° C.-426.7° C.) and injector surface temperatures of 1100° F.-2000° F. (537.8° C.-1093.3° C.). This high temperature may lead to coking of the liquid fuel in the lines and galleries. Over time, the coke may deposit on the lines and galleries and lead to flow restrictions and inoperable conditions.
U.S. Pat. No. 7,117,675 ('675 patent), a patent issued to Kaplan et al. on Oct. 10, 2006, describes a cooling system for gas turbine liquid fuel components to prevent coking. In the system of the '675 patent, a sleeve surrounds a liquid fuel component and a device is used to provide a current of cool air through a space between the liquid fuel component and the sleeve. In the cooling system of the '675 patent the sleeve surrounding the liquid fuel component includes a plurality of spacers for centering the sleeve around the liquid fuel component to create an annulus between the sleeve and the liquid fuel component, through which the current of cool air flows. The current of cool air that is used to cool the liquid fuel component is directed to the annular space using a conduit connected between the cool air device and the sleeve. Although the cooling system of the '675 patent may prevent coking of the liquid fuel within the liquid fuel component, it may have some drawbacks. For instance, using a cool air device to blow cool air around the liquid fuel component may increase the complexity and cost of operating the turbine engine. In addition using individual sleeves to provide an annular space around each liquid fuel component may introduce design complexities when space is limited.